Maps of the large-scale geometrical depolarisation g′ and polarisation angle γ′ for the synchrotron and dust, based on a model of the Galactic magnetic field and density distributions of the energetic electrons and dust grains. These maps are used to correct the dust depolarisation and polarisation angle maps deduced from the 23 GHz polarisation data for the difference in the large-scale structure between synchrotron and dust (see Eqs. (43) and (44)).